-LRB- CNN -RRB- -- The gruesome images are clear . There 's little doubt Syrians suffered a chemical attack last month .

But videos of the aftermath -- including 13 shown to Congress -- do nothing to show who was responsible .

President Barack Obama says he has `` high confidence '' that the regime is to blame -- the strongest position short of confirmation . But his administration has not released hard evidence .

Secretary of State John Kerry says declassifying any more information could endanger `` sources and methods '' of U.S. intelligence gathering .

Britain , France and NATO also blame Syrian President Bashar al-Assad for the horror in a Damascus suburb last month .

Still , as Obama engages in a full-court press to build U.S. support for strikes , some Americans hear echoes of a different basketball analogy : `` slam dunk . ''

That 's how then-CIA Director George Tenet described what turned out to be flawed intelligence that Iraq had weapons of mass destruction in the run-up to the war 10 years ago .

Kerry and Defense Secretary Chuck Hagel were senators at the time .

`` We are especially sensitive , Chuck and I , to never again asking any member of Congress to take a vote on faulty intelligence . And that is why our intelligence community has scrubbed and re-scrubbed the evidence , '' Kerry told Congress .

Some lawmakers remain skeptical .

`` The administration is asking us to go to war on the basis of a four-page document and a 12-page document and none of the underlying evidence , '' Rep. Alan Grayson , D-Florida , complained on CNN 's New Day Saturday .

`` They have evidence showing the regime has probably the responsibility for the attacks . They have n't linked it directly to Assad , in my estimation , '' Rep. Buck McKeon , R-California , told CNN 's State of the Union Sunday .

Beyond a reasonable doubt or no ? U.S. says both

White House Chief of Staff Denis McDonough said the intelligence passes a `` common sense test . ''

`` Now , do we have a picture or do we have irrefutable , beyond a reasonable doubt evidence ? This is not a court of law . And intelligence does not work that way , '' he told CNN 's State of the Union .

But Kerry said last week , `` We can tell you beyond any reasonable doubt that our evidence proves the Assad regime prepared for this attack , issued instructions to prepare for this attack , warned its own forces to use gas masks . ''

Kerry says the amount of information that 's been declassified is `` unprecedented . ''

That information boils down to summaries of what the evidence is .

` Concrete ' evidence : Described , not declassified

Physical , `` concrete '' evidence shows where the rockets came from , when they were fired , and that not one landed in regime-controlled territory , Kerry said .

`` Satellite detections corroborate that attacks from a regime-controlled area struck neighborhoods where the chemical attacks reportedly occurred , '' a declassified White House report says . '' ... The lack of flight activity or missile launches also leads us to conclude that the regime used rockets in the attack . ''

The White House released a map , but no satellite images .

The report also cites `` multiple streams of intelligence , '' without giving specifics .

` Intercepted communications '

`` In the three days prior to the attack , we collected streams of human , signals and geospatial intelligence that reveal regime activities that we assess were associated with preparations for a chemical weapons attack , '' the U.S. report says .

`` Syrian chemical weapons personnel were operating in the Damascus suburb of ` Adra ... near an area that the regime uses to mix chemical weapons , including sarin . On August 21 , a Syrian regime element prepared for a chemical weapons attack in the Damascus area , including through the utilization of gas masks . ''

`` We have a body of information , including past Syrian practice , that leads us to conclude that regime officials were witting of and directed the attack , '' the report says . '' ... We intercepted communications involving a senior official intimately familiar with the offensive who confirmed that chemical weapons were used by the regime on August 21 and was concerned with the U.N. inspectors obtaining evidence . ''

Intelligence shows Syrian chemical weapons personnel were told to cease operations in the afternoon of August 21 and that the regime then `` intensified the artillery barrage '' in the area , the report says .

The material remains classified .

U.S. : Opposition does n't have ` the capacity '

U.S. , British , and French intelligence reports all agree that the opposition could n't have pulled off such an attack .

`` We are certain that none of the opposition has the weapons or capacity to effect a strike of this scale , particularly from the heart of regime territory , '' Kerry told lawmakers .

The White House report points to Syria 's known stockpiles of chemical agents . And it says the United States assesses `` with high confidence that the Syrian regime has used chemical weapons on a small scale against the opposition multiple times in the last year , including in the Damascus suburbs . This assessment is based on multiple streams of information including reporting of Syrian officials planning and executing chemical weapons attacks and laboratory analysis of physiological samples obtained from a number of individuals , which revealed exposure to sarin .

`` We assess that the opposition has not used chemical weapons . ''

In May , a U.N. official said there were strong suspicions that Syrian rebel forces had used sarin gas . But the findings were not conclusive , the U.N. Independent International Commission of Inquiry for Syria said at the time , and the opposition Syrian Coalition condemned any use of chemical weapons . The U.S. State Department said at the time it had no evidence suggesting rebels had used chemical weapons .

Russia , a Syrian ally , says its investigation of a March attack in Aleppo , which apparently involved chemical weaopns , found that the charge used was homemade and similar to projectiles produced by the group Bashaar al-Nasr , part of the opposition Syrian Islamic Liberation Front . Sarin was discovered in samples from the scene , the foreign ministry said .

Assad 's motive unclear

Some experts on the region question why al-Assad would have ordered the attack .

`` Al Assad has no credible motivation to use these weapons at this stage , and in this phase of the conflict . He is not losing , '' writes Ed Husain of the Council on Foreign Relations in a CNN Opinion column . He pointed out that some suggest the al Qaeda-affiliated al-Nusra Front or other opposition elements may have carried out the attack to bait America into the conflict .

William Polk , who served U.S. administrations during the Cuban Missile Crisis and and 1967 Middle East War , writes in The Atlantic , `` I do not see what Assad could have gained from this gas attack . ''

Analyst : ` No way in hell ' U.S. can back up death toll

Questions about the purported death toll in last month 's attack also raises questions about the solidity of the information the U.S. is using .

A preliminary assessment `` determined that 1,429 people were killed in the chemical weapons attack , including at least 426 children , '' the U.S. report says .

`` Secretary Kerry seems to have been sandbagged into using an absurdly over-precise number , '' says Anthony Cordesman , former director of intelligence assessment at the U.S. Defense Department .

Now with the Center for Strategic and International Studies , Cordesman writes on the CSIS website , `` Put simply , there is no way in hell the U.S. intelligence community could credibly have made an estimate this exact . ''

The methodology used to come up with the toll remains classified .

Rebel leaders have said more than 1,300 people were killed . Britain 's Joint Intelligence Organization says at least 350 people were killed . A French report says several sources estimated at least 355 deaths , while others estimate 1,500 .

U.N. wo n't place blame

The United Nations is calling on world leaders not to take action until the results of the U.N. probe are in . But it 's unclear how soon that may be .

And the U.N. team 's mandate was only to determine whether chemical weapons were used -- not by whom .

And Obama says that cat 's out of the bag .

`` Frankly , nobody is really disputing that chemical weapons were used , '' he said .

So , short of a shocking finding that chemical weapons were not used , it 's unclear how much of an effect the U.N. results will ultimately have .

Meanwhile , the Syrian regime continues to insist rebels were behind any chemical attack . But it offers no proof to back that up .

After word broke Sunday that al-Assad had done an interview with Charlie Rose of CBS and PBS denying any involvement in chemical weaopns attacks , Kerry was asked for a response .

`` The evidence speaks for itself , '' he said .

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Americans have not seen the evidence the Obama administration describes

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Two U.S. officials differ on `` reasonable doubt ''

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Obama has `` high confidence , '' the strongest position short of confirmation

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`` No way in hell '' the U.S. knows such a specific death toll , a former defense official says